Many various forms of imaging apparatus and methods are known in the art. The term “imaging apparatus and methods” generally refers to devices and processes for forming visual images on image-carrying media (“imaging media”). One of the most widely known forms of imaging apparatus is that commonly known as the “printer.” One of the most popular types of printers is that known in the art as the electrophotographic printer, which is also often referred to as a “laser printer.”
Laser printers generally function by employing a controlled light source (such as a laser, or light emitting diode) to form a latent version of the desired image on a photoconductive surface. An imaging substance (often in the form of powdered toner) is then applied to the latent image. The imaging substance generally adheres only to the latent image portion of the photoconductive surface, thus forming a visual image. The imaging substance is then ultimately transferred to the imaging media that is most often in the form of paper sheet.
A fuser, or fusing device, is often included in the laser printer. The function of the fusing device is to thermally affix, or fuse, the imaging substance to the imaging media, especially in cases wherein the imaging substance is in the form of powdered toner. The fusing device typically includes a heater configured to heat at least a portion of the fusing device. The heat energy produced by the heater within the fusing device is employed to heat the imaging substance and/or the imaging media so as to form a bond between the imaging substance and the imaging media.
The temperature to which the imaging substance and/or the imaging media are heated is often relatively critical with respect to the quality of the bond between the imaging substance and the imaging media. Thus, the temperature of the heater can be substantially critical with respect to the final image product. The temperature to which the imaging substance and/or imaging media is heated by the fusing device and/or heater can be affected by various environmental variables such as ambient temperature, ambient humidity, media caliper (thickness), and/or several other variables.
Typically, the heater of conventional fusing devices is configured to operate between two predetermined, fixed temperature set points. That is, the fusing device heater is typically configured to operate between an upper temperature set point and a lower temperature set point, between which is an operational temperature range. The upper and lower temperature set points are generally chosen with the goal of enabling the fuser to produce adequate image fusing results under a broad range of environmental conditions and other operational parameters.
Conventional fusing devices also generally include a temperature sensor that is configured to detect the operating temperature of a given portion of the fusing device. Typical fusing devices are configured such that the heater turns on at full power when the sensor detects a fusing device temperature that is below the lower temperature set point. Similarly, typical fusing devices are also configured such that the heater turns completely off when the sensor detects a fusing device temperature that is above the upper temperature set point. In this manner, conventional fusing devices operate over a predetermined temperature range in order to fuse images.
A problem often associated with the aforementioned fuser operational scheme is a phenomenon known as “gloss band.” This phenomenon is manifested as distinctly noticeable variations in the level of toner gloss of a solid image such as a photograph or the like. This gloss band phenomenon can be caused by the typically wide operating temperature ranges of conventional fusing device heaters. The gloss band phenomenon can be especially apparent in cases wherein the heater is turned on or turned off while the solid image is being fused.
In other words, the cause of the gloss band phenomenon can often be the significant change in temperature of the fuser due to the fuser heater being turned on or turned off while cycling between the upper and lower temperature set points during fusing of the image. Developments have been made in the prior art to deal with the phenomenon of gloss band with varying degrees of success. However, such developments often have various negative aspects associated therewith.
Therefore, it can be desirable to provide means for controlling a fusing device so as to lessen the effects of the gloss band phenomenon in an imaging device, wherein such means achieve the benefits to be derived from similar prior art apparatus and methods, but which avoid the shortcomings and detriments individually associated therewith.